[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 231801
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1805 UTC Thu Sep 23 2021

Tropical Weather Discussion for North America, Central America
Gulf of Mexico, Caribbean Sea, northern sections of South
America, and Atlantic Ocean to the African coast from the
Equator to 31N. The following information is based on satellite
imagery, weather observations, radar and meteorological analysis.

Based on 1200 UTC surface analysis and satellite imagery through
1745 UTC.

...SPECIAL FEATURES...

Recently upgraded Tropical Storm Sam is centered near 10.9N 38.1W
at 23/1500 UTC or 1520 nm ESE of the Northern Leeward Islands
moving W at 13 kt. Estimated minimum central pressure is 1003 mb.
Maximum sustained wind speed is 45 kt with gusts to 55 kt.
Satellite imagery depicts a system that is quickly becoming better
organized. The imagery shows that it is a rather-compact, with an
apparent eye-type feature visible. Scattered moderate to isolated
strong convection is noted within about 50 nm of the center,
except 60 nm of the center in the SW quadrant. Similar convection
marks an outer curved band within 30 nm either side of a line from
13N36W to 13N39W and to 11N41W. Peak seas are up to 13 ft within
60 nm of the center in the NE quadrant and within 30 nm of the
center in the NW quadrant. Sam is forecast to become a hurricane
on Fri and be near major hurricane intensity by the end of the
weekend. Please, read the read the latest HIGH SEAS FORECAST
issued by the National Hurricane Center at website-
https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the latest Peter
NHC Forecast/Advisory and Public Advisory at www.hurricanes.gov
for more details.

A gale-force, non-tropical low pressure system, the remnants of
Odette, is located a little more than 520 nm west-northwest of
the westernmost Azores. While showers and thunderstorms remain
limited near the low, only a small increase in this activity could
result in the formation of a subtropical or tropical cyclone
while it moves generally southward over marginally warmer waters
during the next day or so. Strong upper-level winds are expected
to develop over the system beginning tomorrow, which should then
limit further development. Additional information on this system,
including gale warnings, can be found in High Seas Forecasts
issued by the Ocean Prediction Center ocean.weather.gov. Also see
the latest Tropical Weather Outlook at www.hurricanes.gov for more
details.

...TROPICAL WAVES...

A far eastern Atlantic tropical wave has its axis just east of
the Cabo Verde Islands near 22W from 05N to 20N. It is moving
westward at 10 kt. Scattered moderate convection is seen from 05N
to 08N between 19W-22W.

A central Atlantic tropical wave has its axis along 51W from 05N
to 21N, moving westward at 10-15 kt. No significant convection is
noted near the wave axis.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis passes through the the Senegalese coast
near 15N17W to 09N23W to 08N30W. A segment of the ITCZ extends
from 07N40W to 06N48W, and from 06N51W to 06N57W. Aside from
convection associated to the tropical wave described above,
scattered moderate to strong convection is just inland the coast
of Africa within 90 nm south of the trough between 15W-17W.
Scattered moderate to isolated strong convection is within 90 nm
south of the trough between 17W-19W. Scattered moderate convection
is between 120 to 270 nm south of the trough between 23W-27W.

GULF OF MEXICO...

An early season cold front is moving across the northern Gulf, and
as of 15Z it extends from Venice, Florida to 23N90W and to
Veracruz, Mexico. The latest ASCAT data passes along with current
buoy observations indicate fresh to strong north to northeast
winds behind the front. Moderate to fresh northwest winds are
are along and just offshore the coast of Mexico from Veracruz
to Tampico.  Recent altimeter satellite data along with current
buoy observations are showing seas in the range of 3-6 ft behind
the front. Generally, light to gentle breezes and slight seas are
noted south of the front. Satellite imagery reveals a band of

Scattered moderate convection identified to be along and within
about 60 nm north of the front. Similar convection is confined
to the central Bay of Campeche. A drier and stable air mass
under high pressure is following in behind the front.

For the forecast, the front will continue to move southeastward
through tonight, stall from roughly Fort Myers, Florida to the
coast of Veracruz, Mexico near 18N95W Fri, then dissipate Sat.
Fresh to strong winds will follow the front into tonight,
including along the coast of Veracruz where seas may build to
8 ft. Looking ahead, winds and seas will diminish across basin
from Sat and into early next week as high pressure builds over
the northern Gulf.

CARIBBEAN SEA...

A sharp upper-level trough extends from the vicinity of the
southeastern Bahamas to across eastern Cuba and to the
southwestern Caribbean. This trough is acting on an already
very moist and unstable environment resulting in enhanced
scattered moderate to strong convection to exist over the
far south-central and southwestern Caribbean from along the
coast of Colombia and Panama to 13N and between 73W-81W.
A weakened subtropical ridge north of the area continues to
support a pattern of below average winds across the basin.
Moderate trade winds are noted over the southeast Caribbean, with
generally light to gentle trade winds elsewhere. Seas are
relatively low, in the 1-3 ft range, except for slightly higher
seas of 2-4 ft over the far southwestern Caribbean.

For the forecast, Tropical Storm Sam near 10.9N 38.1W 1003 mb at
1500 UTC, moving W at 14 kt. Maximum sustained winds are 45 kt
with gusts to 55 kt. Sam will continue to intensify as it moves
across the Atlantic, becoming a hurricane near 12N45W by Fri
evening, and reaching 55W east of the Leeward Islands by Mon
night. Meanwhile, moderate trade winds will persist over much of
the Caribbean into early next week, becoming fresh over the south-
central Caribbean starting Fri night as high pressure builds east
of the Bahamas.

ATLANTIC OCEAN...

Please read the Special Features section above for details on
newly formed Tropical Storm Sam.

The Cumbre Vieja volcano on the island of La Palma in the Canary
Islands has been erupting since 19/1410 UTC. A significant ash
emission is ongoing in the vicinity of the volcano. Marine and
aviation interests should monitor this on-going situation by
reading Volcanic Ash Advisory issued by Meteo- France at
http://vaac.meteo.fr/volcanoes /la- palma/. The next advisory will
be issue no later than 23/2300 UTC.

As of 15Z, a stationary front extends from near 31N47W to 27N53W
to 29N59W to 27N65W and begins to dissipate to 27N73W. A recent
ASCAT pass depicts moderate to mainly fresh east to southeast
winds north of the stationary front between 56W-59W. A cold front
has moved off the southeastern United States coast and extends
from 31N79W to inland central Florida. A pre-frontal trough
extends from 31N78W to inland South Florida near Stuart.
Satellite imagery shows scattered showers and thunderstorms north
of 29N and between 75W-79W. Broken to overcast multilayered clouds
with embedded areas of rain along with scattered and isolated
thunderstorms are seen north of 25N between 57W-64W. The 1009 mb
remnant low of Peter is near 23N67W. A trough extends northeast
from the low to 26N64W, and southwest from the low to the north-
central coast of Hispaniola. An expanding area of scattered
moderate to isolated strong convection is well removed to the east
of the low from 22N to the stationary front and between 60W- 65W.
Similar activity is also from 19N to 22N between 63W-67W. The
latest ASCAT pass showed fresh to strong southerly winds with
this convective activity. Altimeter data indicates seas up to 7
ft northeast and east of the low from 22N to 28N between 62W-67W.
Seas may be slighter higher in the strong convection.

The post-tropical cyclone remnant 1010 mb low of former tropical
cyclone Rose is near 26N42W. A trough to its southwest extends
from 23N45W to 19N48W. A recent altimeter pass has seas up to 11
ft within about 60 nm in the northwest quadrant of this low. This
attributed to a large area of northerly swell that is producing
seas of 8-12 ft seas north of 22N between 35W-60W. Fresh east to
southeast winds are over the eastern semicircle of the low. The
low will gradually dissipate through Sat. Aside from the features
and related winds and seas already mentioned in this discussion,
moderate to occasionally fresh trade winds are noted across the
basin along with 4 to 6 ft seas in open waters.

For the forecast west of 65W, the remnant low of Peter will
dissipate as it drifts northeast of the region through Fri.
Meanwhile, a cold front extending from 31N79W to central
Florida will stall from near 31N77W to near Fort Pierce, Florida
by tonight, then dissipate through early Sun just before a second
weak front possibly moves into the region early next week. Farther
east, Tropical Storm Sam near is near 10.9N 38.1W 1003 mb at 1500
UTC, moving W at 14 kt. Maximum sustained winds are 45 kt with
gusts to 55 kt. Sam will continue to intensify as it moves across
the Atlantic, becoming a hurricane near 12N45W by Fri evening, and
reaching 55W east of the Leeward Islands by Mon night.

$$
Aguirre
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